Self-adhesive hooks are well known. On the other hand, redetachable hooks of this type which also adhere permanently and firmly are not known. The removal of stuck-on hooks, for example from tiles in the bathroom or in the kitchen, however, is an undertaking in which the substrate can easily be damaged.
Adhesive films for reseparable adhesive bonds which allow an adhesive bond produced with the film to be separable by pulling on the adhesive film in the direction of the adhesion plane are known from DE-OS 33 31 016. High adhesive strength and shear strength can be achieved with such adhesive films, and adhesive bonds can be separated again without further aids, comparable to opening a zip fastener, or even better comparable to opening a preserving jar: the rubber seal is pulled out of the sealing joint by the tab.
In practice, however, considerable disadvantages have manifested themselves when such adhesive films are used. On the one hand, it is a product which requires explanation. Those who have not previously used such an adhesive film easily tend to stick the components of the joint to one another in such a way that the adhesive film disappears between the components of the joint and no longer projects out so that it can no longer be pulled on: irreversible bonding is the consequence, with corresponding disappointment. However, the disappointment is just as great if, when used correctly, the adhesive film then tears when pulled on: here also an irreversible bonding is the consequence. The advantage of a reseparable adhesive bond which can be achieved without damage to the components of the joint in the simplest manner merely by pulling turns into a drastic disadvantage, since precisely the components of the joint which are to be separated again are now bonded permanently. The only course is usually to destroy the components of the joint.
The inventors of DE-OS 33 31 016 also recognized the problem of tearing during pulling and paid it particular attention. On page 4, centre, there is accordingly a certain ratio of peel strength to tear load: the tear load should always be greater than the peel strength, and for safety reasons the peel strength should be in a ratio of 1:2 to 1:3 to the tear load.
In practice, however, it has been found that this precaution is often not sufficient. Substrates bonded on an exhibition site, which are to be separated again after the end of the exhibition, can no longer be separated because of tears. This is likewise the case with calendars or advent decorations bonded to a window. Posters or pictures fixed to the wall in this way also become irreversible wall decoration as soon as the adhesive film tears off when pulled. The damage is considerable and the customer is lost. Even the use of still thicker adhesive films, as recommended by DE-OS 33 31 016, does not help to prevent such tears.
DE-PS 37 14 453 also discloses the use of such an adhesive film, called a strip tape therein, for allowing the non-destructive removal of training explosives from training objects. Here also, a tongue 6 is allowed to project out from the side of the adhesive joint; this tongue can be pulled in order to separate the bond again in this way. Tears also occur in this application in practice.